Impact of disease management practices on disease incidence, yield and proximate composition of sweet basil (Ocimum basilicum L.)

Introduction

Sweet basil (Ocimum basilicum L.) belonging to the family Lamiaceae is one of the most important aromatic plants cultivated for its essential oil, medicinal properties, and pharmaceutical applications. The crop holds a prominent position in the genus Ocimum due to its diverse therapeutic uses and high commercial value (Reis et al., 2007) [17] . In India, sweet basil is grown commercially in states such as Madhya Pradesh, Punjab, Uttar Pradesh, and Jammu & Kashmir, with expanding cultivation driven by increasing demand in national and international markets (Patel and Kushwaha, 2013) [15] . Dry root rot of sweet basil is caused by Macrophomina phaseolina (Tassi, 1901) [20] Goid., a soil-borne, necrotrophic pathogen with a wide host range. The pathogen is widely distributed in tropical and subtropical regions and is known to infect more than 500 plant species (Das and Indira, 2008). Disease development is favored by high temperature and moisture-stress conditions, often resulting in considerable yield losses (Tesso et al., 2005) [21] . The pathogen can infect the crop at different growth stages, from seedling to maturity, and affects various plant parts including roots, stems, leaves, pods, and seeds (Mukharji and Bhasin, 1986) [13] . Typical symptoms include dark brown to grey lesions on the stem, followed by wilting, defoliation, and eventual plant death (Reis et al., 2007; Abawi and Pastor-Corrales, 1990) [17,2] Macrophomina phaseolina is a highly persistent soil-borne pathogen capable of surviving as microsclerotia for extended periods in dry soil conditions. These survival structures enable rapid infection when favorable conditions occur; making disease management difficult through single control measures (Sinclair, 1989) [18] . The lack of resistant cultivars and the wide host range of the pathogen further complicate management strategies.

Integrated disease management (IDM) has emerged as a viable approach for controlling soil-borne diseases by combining biological, botanical, and chemical methods. Botanicals and plant oils have gained attention due to their antifungal activity and environmental safety. Several plant extracts have been reported to inhibit mycelial growth of M. phaseolina by disrupting fungal metabolism and cell wall integrity (Sindhan et al., 2002; Khaire et al., 2018) [19,9] . Essential oils from neem and tulsi are widely recognized for their antifungal properties. The effectiveness of neem oil against soil borne pathogen has been reported by Kumar et al. (2019) [11] . Biological control agents such as Trichoderma viride and Pseudomonas fluorescens are widely recognized for their antagonistic activity against M. phaseolina. These bioagents suppress pathogen growth through competition, antibiosis, mycoparasitism, and induction of host defense enzymes (Anand et al., 2009) [3] . Induced systemic resistance plays a crucial role in disease suppression by enhancing the activity of defense-related enzymes such as peroxidase, chitinase, and polyphenol oxidase, thereby limiting pathogen colonization (Kuc, 1982; Ye et al., 1990) [10,23] . In modern agriculture, fungicides play an important role in the management of plant diseases. Recent studies have also included the new-generation fungicides with improved modes of action and lower risk of resistance, which have shown effectiveness against several soil-borne pathogens, including Macrophomina phaseolina (Gandhi and Rao, 2019; Karibasappa et al., 2020) [6,8] . Apart from disease suppression, IDM practices influence crop growth and quality. Disease management strategies not only reduce disease incidence but also affect proximate composition parameters such as protein, fibre, carbohydrate, oil, and ash content in plants. Improvement in crop quality through effective disease management has been reported earlier, highlighting the importance of evaluating management practices beyond disease control alone (Sohalbiani et al., 2011) [1] . Considering the economic importance of sweet basil and the destructive nature of dry root rot, there is a need to identify effective, environmentally sustainable disease management strategies. Therefore, the present study was undertaken to evaluate different biological, botanical, and chemical alternatives under integrated disease management practices for controlling dry root rot of sweet basil caused by Macrophomina phaseolina, with special emphasis on disease reduction and improvement in crop quality parameters.

Materials and Methods

Experimental Site

The field experiment was conducted during the kharif season at the experimental field of ACRIP on MAP&B, Department of Plant Physiology, Jawaharlal Nehru Krishi Vishwa Vidyalaya (JNKVV), Jabalpur, Madhya Pradesh, India in 2020.

Experimental Design and Crop Details

The experiment was laid out in a Randomized Block Design (RBD) with seven treatments and three replications. Each plot measured 3 × 2 m², with a row-to-row spacing of 40 cm and plant-to-plant spacing of 30 cm. A local sweet basil (Ocimum basilicum) variety was used for the study. Sowing was done as per recommended agronomic practices.

Source of Bioagents and method of application

Bioagents such as Trichoderma viride and Pseudomonas fluorescens were obtained from authenticated laboratory cultures maintained at JNKVV, Jabalpur. Talc-based formulations were used for soil and foliar applications. Farmyard manure (FYM) was thoroughly mixed with talcbased formulations of T. viride and P. fluorescens and incubated for 7 days under shade conditions before application. The enriched FYM was applied uniformly to the soil at planting time. Foliar sprays of bioagents, botanical oil, and fungicides were applied using a knapsack sprayer at recommended concentrations. Sprays were initiated at the onset of disease symptoms and repeated at 15-day intervals.

Treatment Details

The following integrated disease management treatments were evaluated under field conditions:  T 1: Soil application of FYM (1 kg/m²) enriched with Trichoderma viride + Pseudomonas fluorescens (each @ 2.0%) at planting  T 2: T 1 + three foliar sprays of P. fluorescens (2.0%) at disease onset  T 3: T 1 + three sprays of neem oil @ 300 ppm  T 4: T 1 + three sprays of P. fluorescens (2.0%) + neem oil @ 300 ppm  T 5: T 1 + three sprays of Trifloxystrobin 25% + Tebuconazole 50% @ 0.1% at 15-day intervals  T 6: T 1 + three sprays of Copper oxychloride @ 0.25% at 15-day intervals  T 7: Control (untreated)

Observation on Disease Incidence

Disease incidence was recorded periodically by counting the number of infected plants in each plot. Percent disease incidence was calculated using the formula given by (Waller et al., 2002) [22]: Disease incidence = Number of infected plants total number of plants × 100

Yield Assessment

Harvesting was carried out at crop maturity. Yield was recorded on a plot basis and expressed in appropriate units after conversion.

Determination of Quality Parameters

Moisture content of sweet basil samples was determined by oven-drying method following AOAC (2010) [4] procedures. Crude protein content was estimated using the Kjeldahl method and calculated by multiplying nitrogen content with a conversion factor. Crude fiber content was determined following standard AOAC (2010) [4] methodology involving acid and alkali digestion. Total ash content was estimated by incinerating dried samples in a muffle furnace at 550-600 °C until constant weight was obtained. Essential oil was extracted from fresh leaves using hydro-distillation method with a Clevenger apparatus. Oil content was expressed as percentage based on fresh weight of plant material.

Statistical Analysis

The field data were subjected to analysis of variance (ANOVA) appropriate for Randomized Block Design. Treatment means were compared using critical difference (CD) at 5% level of significance. Statistical analysis was performed following standard procedures.

Results and Discussion

Field evaluation of integrated disease management revealed significant differences among treatments with respect to disease incidence and disease control. Treatment T 1 recorded the minimum disease incidence (5.33%) along with the maximum disease control over check (68.05%). This was followed by treatments T 2 and T 3 , which showed moderate reduction in disease incidence with disease control of 43.98% and 31.94%, respectively. Higher disease incidence and lower disease control were recorded in the remaining treatments, with the lowest disease control over check observed in T 4 . The untreated control recorded the maximum disease incidence. The superior performance of treatment T 1 under field conditions indicates the effectiveness of antagonistic properties of the bioagents against the pathogen. Similar observations were reported by Rathore et al. (2020) [16] , Godara and Suresh Kumar (2018) [7] , and Manjunatha et al. (2013) [12] . Treatment T 1 , comprising only bioagents, exhibited superior performance, likely due to their strong antagonistic activity against the pathogen. The relatively lower effectiveness of treatments combining bioagents with other inputs may indicate possible interactions among the applied components. However, such interactions were not examined in the present study, and further research is required to assess their compatibility under field conditions. [12] , Rathore et al. (2020) [16] and Godara and Suresh Kumar (2018) [7] . The lowest yields observed in the untreated control plots further confirm the detrimental impact of dry root rot on crop productivity under field conditions.

Effect of IDM on proximate composition

The proximate composition of healthy sweet basil leaves was analyzed using standard methods of A.O.A.C. (2010). Among the quality parameters studied, essential oil content, which is the major economic component of sweet basil, was found to be significantly higher in treatment T 1 (0.97%). In contrast, other proximate components such as moisture, fibre, protein, ash, and carbohydrate content did not show significant variation among the treatments and were statistically comparable with the control. The absence of significant variation in most proximate composition parameters indicates that the applied disease management practices did not adversely affect the quality of sweet basil, while the increase in essential oil content under T 1 suggests a positive influence of bioagent-based treatment on crop quality.

Conclusion

Under field conditions, soil application of FYM (1 kg/m²) enriched with Trichoderma viride and Pseudomonas fluorescens (talc-based formulations @ 2.0%) at planting proved most effective in reducing dry root rot incidence of sweet basil. This treatment also resulted in maximum yield of leaf, inflorescence, and stem, while maintaining standard quality parameters. The highest leaf oil content, the most important economic trait of sweet basil, was also recorded under this treatment. The results indicate that integration of selected bio-agents with organic amendments offers an ecofriendly and sustainable strategy for managing dry root rot and improving crop productivity. However, multi-season and multi-location validation is required before large-scale adoption.

Acknowledgement

AcknowledgementThe authors are thankful to Jawaharlal Nehru Krishi Vishwavidyalaya, Jabalpur, and the All India Coordinated Research Project (AICRP) on Medicinal and Aromatic Plants for providing field facilities to conduct the present investigation.

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